AP Physics 1 2018 Free Response Solutions
TLDRIn this video, the presenter walks through the 2018 AP Physics free response questions, offering insights into problem-solving strategies for various physics concepts. The discussion covers topics such as spacecraft motion, resistivity of conductive materials, rotational inertia, wave properties, and spring-mass oscillators. The presenter provides detailed explanations and graphical representations to help viewers understand the underlying physics principles and how to approach solving the problems.
Takeaways
- π The video discusses the 2018 AP Physics exam's free response questions, providing insights into tackling them.
- π The first question examines a spacecraft in a circular orbit, highlighting the force of gravity and deriving Kepler's third law.
- π For the second question, students mold conductive dough into cylinders, applying Ohm's law to determine resistance and resistivity.
- π The third question explores the effect of temperature on the resistivity of dough cylinders, suggesting an experiment to measure changes with temperature.
- π Question four involves analyzing a transverse wave's properties, including instantaneous velocity and acceleration at specific points.
- ποΈ In the final question, a spring-block oscillator's period and amplitude are examined when an additional mass is added to the system.
- π The resistivity of the dough cylinders does not depend on their shape, but on their material properties.
- π The video provides a step-by-step approach to solving the problems, emphasizing the importance of understanding the underlying physics concepts.
- β±οΈ Time management is crucial when taking the AP Physics exam, as students must complete all questions within the allotted time.
- π― The video encourages students to review the official solutions and scoring guides for a deeper understanding of the exam's expectations.
- π The 2018 AP Physics free response test is considered solid, covering a broad range of topics and providing a fair assessment of students' knowledge.
Q & A
What is the main topic of the video?
-The main topic of the video is a walkthrough of the 2018 AP Physics 1 free response exam questions.
How does the speaker begin the video?
-The speaker begins the video by welcoming everyone and stating the purpose of the video, which is to look at the 2018 AP Physics 1 free response exam questions.
What is the first problem discussed in the video?
-The first problem discussed in the video involves a spacecraft moving in a circular orbit around the Earth and the forces acting on it.
What force does the speaker identify as acting on the spacecraft in orbit?
-The speaker identifies the force of gravity as the only force acting on the spacecraft in its circular orbit.
How does the speaker derive the equation for the orbital period in part 1b of the first problem?
-The speaker derives the equation for the orbital period by using the centripetal force equation (MV^2/R = G*(m_spacecraft * m_earth)/R^2) and solving for the period (T), resulting in T = 2Ο*β(R^3/(G*m_earth)).
What happens to the period of a spacecraft's orbit when a second spacecraft with mass 2m is introduced in the same orbit in part 1c of the first problem?
-The period of the orbit does not change when a second spacecraft with mass 2m is introduced, as the period is independent of the mass of the spacecraft.
What material is suggested for making conductive dough in the second problem?
-The speaker suggests using salt instead of sugar to make the dough conductive, as sugary dough is not very conductive.
How does the speaker propose to graph data to find the resistivity of the dough cylinders in part 2 of the second problem?
-The speaker proposes to graph resistance times cross-sectional area (RA) on the y-axis and length (L) on the x-axis to determine the resistivity of the dough cylinders.
What is the speaker's conclusion about the effect of shape on resistivity in part 2b of the second problem?
-The speaker concludes that the resistivity does not depend on the shape of the dough, as it is a material property and resistivity equals resistivity times length over cross-sectional area, which is the same for both rectangular and cylindrical resistors.
How does the speaker describe the experimental procedure to determine the effect of temperature on resistivity in part 2c of the second problem?
-The speaker describes an experiment where a cylindrical dough is placed on a hot plate with a multimeter attached to measure resistance and a thermometer to measure temperature, recording the temperature and resistance every 30 seconds to observe changes in resistivity with temperature.
What is the main concept tested in the third problem about a spinning disc?
-The main concept tested in the third problem is the relationship between constant torque, angular acceleration, and rotational inertia, as well as the graphical representation of these quantities over time.
How does the speaker analyze the effect of adding oil to reduce friction in part 3c of the third problem?
-The speaker analyzes the effect of adding oil by describing how the graph of angular acceleration over time will change from a straight line to a curve as the friction decreases, leading to a decrease in angular acceleration.
Outlines
π Spacecraft Motion and Orbital Period
The paragraph discusses the analysis of a spacecraft moving in a clockwise circular orbit around the Earth. The focus is on identifying the forces acting on the spacecraft, which is primarily the gravitational force. The speaker then attempts to derive an equation for the orbital period in terms of the spacecraft's mass, Earth's mass, radius, and physical constants. This derivation is based on the concept of centripetal force and leads to an equation that resembles Kepler's third law. The discussion also covers the impact of introducing a second spacecraft of mass 2m into the same orbit and explains why the orbital period remains unchanged. Lastly, the paragraph explores the change in speed of the first spacecraft when it moves into a new orbit with a larger radius, concluding that the speed decreases as the radius increases.
π Electrical Resistivity of Conductive Dough
This paragraph delves into an experiment involving conductive dough, which is molded into cylinders and tested for resistance. The goal is to determine the resistivity of the material. The speaker outlines the process of plotting resistance against the cross-sectional area and length of the cylinders to derive the resistivity. The paragraph also addresses the second part of the question, which asks about the impact of shaping the dough into rectangular forms instead of cylinders. The speaker clarifies that resistivity is a material property and does not depend on the shape of the dough. The paragraph concludes with a proposed experimental procedure to determine the effect of temperature on the resistivity of the dough cylinders, suggesting a method that involves heating the dough and measuring changes in resistance.
π Graphing Angular Acceleration and Inertia
The paragraph focuses on the analysis of angular acceleration and rotational inertia using graphical methods. The scenario involves a disc spinning around an axle, where friction between the axle and the disc exerts a constant torque. The speaker explains how to graph the disc's angular acceleration over time and derive the rotational inertia from the slope of the graph. The paragraph also discusses how the torque would change when oil is applied to reduce friction, altering the graph's shape. The speaker then selects the best mathematical model to represent the torque based on the given options and explains the rationale behind the choice.
π Wave Motion and Displacement Analysis
This paragraph examines the motion of a transverse wave traveling along a string, with specific attention given to two points, P and Q. The speaker describes how to determine the instantaneous velocity and acceleration of a point on the wave at a given moment. A graphical representation is used to illustrate the position of the wave at a later time, with the speaker providing a step-by-step explanation of how to plot the wave's new position. The paragraph concludes with an analysis of the total distance traveled by point P over one full period of the wave, emphasizing the importance of units in calculations.
π Spring-Block Oscillator with Mass Addition
The final paragraph of the script discusses a spring-block oscillator system, where a second block with twice the mass of the original is added to the system. The speaker calculates the new period and amplitude of oscillation, comparing them to the original values. The explanation involves the application of conservation of energy and momentum principles. The speaker concludes that the new amplitude will be less than the original due to the decrease in maximum kinetic energy, which in turn affects the spring's potential energy at maximum amplitude. The paragraph ends with a reflection on the overall difficulty and reasonableness of the 2018 AP Physics free response test.
Mindmap
Keywords
π‘Circular Orbit
π‘Gravity
π‘Orbital Period
π‘Centripetal Force
π‘Resistivity
π‘Conductive Dough
π‘Resistance
π‘Angular Acceleration
π‘Torque
π‘Rotational Inertia
π‘Transverse Wave
π‘Spring Block Oscillator
Highlights
The discussion begins with an analysis of a 2018 AP Physics free response exam question about a spacecraft in a circular orbit around Earth.
The force acting on the spacecraft in a circular orbit is identified as the force of gravity, directed towards the center of the orbit.
Kepler's third law is derived to find the orbital period in terms of the spacecraft's mass, Earth's mass, the radius, and physical constants.
It is noted that the orbital period does not depend on the mass of the spacecraft, which is a key concept in understanding orbital mechanics.
The speed of the spacecraft is shown to be dependent on the radius of the orbit, with an increase in radius resulting in a decrease in speed.
The concept of resistivity and its calculation through the use of conductive dough cylinders is explored.
A method for graphing resistivity is proposed, involving plotting resistance times cross-sectional area against length to determine the slope, indicative of resistivity.
The experiment's adaptability to different shapes, such as rectangular resistors, is discussed, with the conclusion that resistivity is a material property and does not change with shape.
An experimental procedure to determine the effect of temperature on the resistivity of dough cylinders is suggested, involving measuring resistance and temperature changes.
The analysis of a spinning disc subjected to a constant torque is presented, with a focus on the relationship between torque, rotational inertia, and angular acceleration.
A graphical representation of the disc's angular acceleration over time is provided, highlighting the impact of reducing friction on the system's dynamics.
A wave traveling along a string is analyzed, with the instantaneous velocity and acceleration of points on the wave being key elements of the discussion.
The total distance traveled by a point on the wave over one full period is calculated, offering insight into wave propagation.
A spring-block oscillator system is examined, with the period and amplitude of oscillation being critical factors in understanding the system's behavior.
The impact of adding a second, more massive block to the spring-block oscillator is discussed, particularly in terms of changes in the system's period and amplitude.
The concept of energy conservation is applied to explain the reduced amplitude in the two-block system compared to the original setup.
The exam's questions are deemed reasonable and well-rounded, covering a broad scope of AP Physics concepts in a manner that reflects the actual exam format.
The importance of reviewing the official College Board scoring guides to understand how each question is scored is emphasized for test preparation.
Transcripts
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